1. Field of the Invention
The present invention relates to adsorbent processes of air purification. More particularly, the invention is directed to a monitor apparatus for signaling the relative state of adsorber bed saturation.
2. Description of the Prior Art
Atmospheres surrounding chemical processing facilities are frequently contaminated with small quantities of chlorine and hydrogen sulfide. Although of low concentration, such contaminants are extremely destructive of certain instrumentation and data processing control equipment.
Responsively, vulnerable instruments and data processing equipment are placed in environmentally controlled enclosures which are ventilated by purified air.
To remove the destructive compounds from the localized atmosphere, a ventilation flow stream drawn from the contaminated ambient air is forced through a bed of particulate activated carbon which adsorptively retains the contaminant compounds.
In time and usage, a given adsorber bed will saturate its adsorption capacity for a particular compound and must be either replaced or regenerated. Operating experience with adsorber bed technology has revealed that such saturation progresses through the bed as a wave band traveling parallel with the air flow stream direction. Air flow within the adsorber bed passing through the saturation band is completely free of contaminant compound. Air flow behind the moving band front is contaminated by degree of proximity to the front. As the actively adsorbing band advances through the adsorber bed, adsorbent behind the band is saturated and therefore no longer contributes toward contaminant removal from the flow stream.
To track progress of the actively adsorbing band for the purpose of predicting the approximate time of total bed saturation, the prior art has used several indicator or monitor techniques. One such technique has been a copper, silver or gold plated monitor rod inserted up the bed depth. Cl.sub.2 and H.sub.2 S corrode the metal within and behind the actively adsorbing band front. Positional advancement of a visually discerned line of discoloration is correlated to time differentials to predict complete saturation of the adsorber bed. Record keeping necessitates removal of the monitor rod from the adsorber bed to measure the location of the line of color discontinuity. Such discoloration is assumed to represent corrosion. However, the degree or rate of discoloration is highly influenced by the relative humidity of the air flow stream. Consequently, corrosion on copper cannot be gauged solely by discoloration.
Another prior art bed monitoring technique relies upon the measurement of electrical characteristic changes within a metallic tag imbedded within the adsorbent bed. As the metal tag corrodes responsively to Cl.sub.2 or H.sub.2 S exposure, electrical resistance across the corroded tag increases. This evaluation technique is also highly responsive to relative humidity.
A third prior art bed monitoring technique engages the use of color responsive permeable membranes across sample air flow streams drawn from predetermined bed positions. These permeable membranes are usually filter papers impregnated with reactive compounds selected for chromatic change properties responsive to a second compound exposure, i.e. H.sub.2 S and Cl.sub.2. In some cases, X-ray fluorescent techniques are required to evaluate the membranes. These impregnated filters are arranged in a stacked series that requires disassembly of the monitor unit to evaluate the report.
An objective of the present invention, therefore, is to provide a chromatic bed monitor unit that requires no disassembly for contamination appraisal.
Another object of the present invention is to provide an adsorber bed monitor that presents all impregnated membranes in a single, continuously visible plane.
Another object of the present invention is to provide a series flow sequence of chromatically responsive, permeable membranes wherein a first membrane in the sequence removes compounds that give misleading chromatic responses from a subsequent membrane in the sequence.